This program functions as a regional center for studies on muscle. The major areas of investigation include the development, molecular organization and function of contractile and regulatory proteins, and the mechanics, energetics and excitation-contraction coupling mechanisms of cardiac, smooth and skeletal muscle. The general scope of this work is summarized in the Research Objectives of HL15835-06-10. The objectives of the present proposal are: 1) to relate the kinetics of actomyosin ATPase to the attachment and detachment rates of cross bridges in single isolated muslce fibers with the aid of laser-induced, rapid ATP pulses from "caged ATP" and through 18O exchange studies, 2) to continue the development of high resolution X-ray mapping and electron energy loss spectroscopy of muscle, and to conduct electron probe analytic studies of the Ca ions content of the organelles (mitochondria, SR) of cardiac, skeletal and vascular smooth muscle, 3) to develop and apply novel preparatory techniques combined with rapid freezing for the study of the molecular architecture of the internal membrane and filament systems of muscle.